I would try in the units one at a time without any try-in cement to check marginal fit. I would try in the crowns on tooth #8 and #9 together to verify the contacts are correct and are not keeping them from seating. I would then load the veneers on tooth #7 and #10 with try-in cement to verify they will seat while tooth #8 and #9 are seated.
I always seat tooth #8 and #9 first, and since they are Captek crowns, I would use a resin-reinforced glass ionomer like RelyX™ Luting Plus cement (3M™ ESPE™; St. Paul, Minn.) or GC Fuji Plus™ (GC America; Alsip, Ill.). Once those have been cemented and the excess cement has been cleaned, it’s time to move on to the veneers.
You should rinse the water-soluble try-in paste out of the veneers for tooth #7 and #10, and then dry them to verify you can see the etched internal surface of the veneers. If you can’t, you should re-etch them with a 6 to 10 percent hydrofluoric acid for 60 seconds, and then rinse. You would then place the ceramic silane solution of your choice (Kerr Silane Primer [Kerr; Orange, Calif.], for example) and evaporate it after about 10 seconds. Place a thin layer of bonding agent (adhesive) from a two-bottle system (such as OptiBond® [Kerr]) and air thin.
Because these are minimal-prep veneers, and by definition confined to the enamel, etch the enamel surface with your choice of phosphoric acid (I use Ultra-Etch® [Ultradent; South Jordan, Utah]). Rinse after 15 seconds. We don’t need a dentin bonding agent, so I would use the same bonding agent we placed in the veneer. For me, it’s the adhesive from the two-bottle OptiBond system. Air thin that once you have brushed it onto the tooth, and load the veneers with your preferred resin cement. For me, that is the translucent shade of NX3 Nexus® Third Generation light cure cement (Kerr). Seat one of the veneers by sliding it into place with facial and incisal pressure. Tack cure it for two to three seconds to get the cement to its gel stage, clean the excess, then finish curing and repeat for the other side.